Ethernet controllers, in particular stand alone Ethernet Controllers, are designed to serve as an Ethernet network interface for any type of microprocessor or microcontroller. Such a controller can have a fairly large memory and may include a dedicated interface such as a serial peripheral interface (SPI) bus. In some embodiments, such an Ethernet controller may also be integrated in a microcontroller using the SPI bus or any other capable interface connection. The Ethernet controller handles all communication protocols and comprises a large buffer for intermediate storage of incoming and outgoing messages. The stand alone or integrated Ethernet controller handles coordination of incoming and outgoing data packets as well as packet filtering. It may further comprise an internal direct memory access (DMA) module for fast data throughput and hardware assisted checksum calculation. The communication of an Ethernet controller with a microcontroller or microprocessor can be established interrupt driven. A microcontroller or microprocessor may communicate and control the Ethernet controller via the SPI interface. To this end, the Ethernet controller comprises a system control unit that interprets ands executes a limited amount of commands received through the interface. Many control functions can be provided through a plurality of control registers. In an Ethernet controller with an SPI interface, a commands are 8-bit wide and, thus, only a limited number of bits, for example five bits, can be used to address a register. However, this allows only access to 32 different registers. If an Ethernet controller has, for example, over a hundred registers, direct access to all registers requires more than one command byte. To provide fast read and write access to the registers, a banking scheme is often used. However, each bank is limited in the number of registers and important registers that need to be always accessible need to be mirrored to all banks. This further limits the number of additional usable registers.